Multi-component plastic housing

ABSTRACT

A multi-component housing having a length and comprising at least a first component comprising a first plastic material, a second component comprising a second plastic material, and a third component comprising a third plastic material. The housing includes at least one tolerance-elimination element made of the second plastic material and longitudinally attached to the first component along the housing&#39;s longitudinal axis. The tolerance-elimination element has an average length extending parallel to the housing&#39;s longitudinal axis, which average length is at least ten times less than the length of the housing. The third component at least partially forms an outer surface of the housing, so that the tolerance-elimination element is at least partially overmolded by the third plastic material.

FIELD OF THE INVENTION

The present disclosure is concerned with the mass manufacturing ofmulti-component plastic items made by injection molding, such as, e.g.,those used as components for various power/electric tools, toothbrushes,and the like.

BACKGROUND OF THE INVENTION

Mass production of multi-component plastic items, such as, e.g.,generally tubular toothbrush handles and other similar multi-componentplastic elements, are typically made by a multi-step injection-moldingprocess, wherein multiple molding steps are performed at multipleinjection-molding stations. In the context of mass production ofidentical articles, those multi-component plastic elements, which willlater become part or parts of the finished articles, are required tohave a certain size and shape uniformity. This uniformity can be definedby the extent to which minute variations in corresponding shapes andsizes among the identical parts being successively injection-molded canbe tolerated. The concern for uniformity is particularly important whenthe manufacturing process requires various molds to be involved—andbecomes even more pronounced when multi-component parts that arerequired to be virtually identical are manufactured at multiplelocations, which may have somewhat different manufacturing conditions aswell as equipment and suppliers of the plastic material.

Virtually all plastic materials, after having being heated to beliquefied—and then cooled and solidified, typically shrink, therebyreducing their physical dimensions. This phenomenon is commonly referredto as “mold shrinkage.” Since identical or similar plastic materials areexpected to shrink proportionally to the same or similar degree, plasticparts having relatively greater dimensions shrink, in absolute numbers,to a greater extent relative to parts having relatively smallerdimensions. At the same time, while a shrinkage rate or percentage ofshrinking for a certain material, such as, e.g., polypropylene (PP) orpolypropylene (PE), can generally be known, it may be difficult toaccurately predict the exact mold shrinkage beyond a “typical” shrinkagerate known for these materials. And the greater the dimension of theplastic material subjected of shrinkage, the more difficult it is toprecisely predict the exact amount of shrinkage. This difficulty can beattributed to the following factors.

Shrinkage of a plastic part made by molding is believed to be likened tolinear thermal contraction or expansion. When a mass of molten polymeris subjected to cooling, it contracts as the temperature drops. Holdingpressure may be used to minimize shrinkage—but this can be effectiveonly as long as the gate(s) remains open. If the polymer is homogeneous,all parts are expected to shrink proportionally even after the pressureis removed or the gates freeze off. This is what generally occurs withamorphous polymers, such as, e.g., polystyrene, polycarbonate, ABS, etcetera.

But PP and PE typically behave differently. Unlike amorphous polymers,PP and PE are not homogeneous materials—but are, instead,semi-crystalline materials, having a structure containing both amorphouscomponents and crystalline components. Crystals normally shrink at rateshigher than the rates at which the amorphous components shrink.Therefore, as these semi-crystalline materials, containing bothamorphous and crystalline components, cool and solidify, they shrink atdifferent rates. This imbalance typically results in a net increase inshrinkage and introduces sensitivity to molding parameters that may haveadditional effects on the shrinkage.

Another factor influencing shrinkage is believed to be linked to theviscoelastic characteristics of high-molecular-weight polymer melts in amold. Long molecular-weight chains are stretched in the mold—and thusexperience stress therein. During subsequent cooling, this stress isrelieved, and the chains tend to relax. This relaxation influences theshrinkage, especially in differential flow directions. Both the averagemolecular weight and the molecular-weight distribution impact thisaspect of mold shrinkage. Other variable factors that may influenceshrinkage include thermal history of the molding, e.g., the melttemperature and cooling rate, as well as a thickness of the part beingmolded, gate dimensions, and other relevant factors.

In addition, plastic parts having a complex geometry, and especiallythose parts that comprise multiple layers of different plasticmaterials, tend to have differential shrinkage rates in differentsections of the part. Although this phenomenon is largely pronouncedduring molding of parts having differential wall thickness, it may occureven in parts having relatively uniform wall thickness. The latter canbe attributed, among other things, to non-uniform cooling and/ornon-uniform filling patterns.

During a molding process of a multi-component part, such, e.g., as atoothbrush-handle housing or a power-tool housing, involving differentmolds, it may be necessary to place the part being made at differentfixation geometries, i.e., mold cavities and/or mold cores. Molds havingcores are naturally required for producing molding parts having agenerally tubular geometry. A change of mold cavities is typicallyrequired to form a tubular part having multiple layers or componentsmade of multiple plastic materials. A change of cores can also berequired if one wishes to add one or more characteristics, geometries,or components to the inner surface of the tubular part being made, i.e.,an area that is in contact with the core. Another reason for the changeof the core in some instances may be dictated by a requirement that afollowing molding step is to be conducted on additional moldingequipment incorporating another core.

If the part molded on a first molding tool needs to be transferred to asecond molding tool for further molding/overmolding, this part'spositioning in the second molding tool needs to be exact, allowing forvery small tolerances. As used herein, the term “tolerance” refers to anallowable amount of variation of a specified measurable dimension,particularly a length dimension of a multi-component housing or any partthereof. As no item or any of its parts can be produced havingdimensions precisely to the exact nominal value, tolerances aretypically assigned to parts for manufacturing purposes, as boundariesfor acceptable build.

Hence, there are acceptable degrees of deviation from the exact nominalvalue, suitable for a particular machine, process, or part. Amanufactured part having dimensions that are out of tolerance will beunlikely a usable part for the intended purpose. Tolerances can beapplied to any dimension. In the present context, lengthwise tolerancesof a plastic part of parts, made by an injection-molding process, are ofa particular interest. The exact positioning of the plastic part insidea mold is required to enable a reliably stable process and accuratetouch-up lines between various molded components. The latter may greatlyinfluence functional and aesthetic aspects of the finished product.

When the plastic part molded in one mold cavity is transferred toanother mold cavity for further overmolding by another plastic material,one needs to take into account the fact that the length of the moltenplastic part will likely change after it is cooled and solidified—as aresult of the plastic material's shrinkage caused by cooling. If theshrinkage is significant, resulting in the solidified part being tooshort for a particular mold cavity, the mold parts intended to contactthe part's surfaces may not reach those surfaces to provide a securecontact therebetween. The resulting undesirable empty spaces between themold parts and the part's surfaces will likely cause “flashes” of theplastic material that is subsequently molded over the part that is tooshort.

Reversely, if the part being molded is too long for a subsequent moldcavity, the compression caused by the mold cavity's surfaces in contactwith the part may crush the edges of the part being made. In addition,the mold may not be able to close completely and securely if the partdisposed therein is too long for this mold. The latter may also lead toproblems with the mold tool itself, including its premature ware anddamage.

The mass production of the increasingly complex molded parts, such as,e.g., a multi-component handle part for a power toothbrush, requiressuccessive changes of molds and/or mold cores. Such changes arerequired, e.g., when a previously molded part comprising a first plasticmaterial needs to be at least partially overmolded with at least asecond plastic material; and then the composite part, comprising thefirst and second plastic materials, needs to be further at leastpartially overmolded with at least a third plastic material, andpossibly fourth plastic material, and so on.

These multiple successive molding steps require an exact positioning ofthe part being manufactured (i.e., molded/overmolded) step-by-step inevery mold cavity and/or mold core that needs to be used in the process.To accomplish such an exact positioning, the manufacturer needs to makesure that the size and geometry of all elements, including the partbeing manufactured and the mold components used, match one another witha high-level precision, allowing for very small tolerance. Thesetolerances are often hard to achieve, particularly with respect toplastic parts affected by shrinkage, as is explained herein.

The exact positioning of the part being manufactured is particularlyimportant in the context of a mass production that may take place atdifferent locations. Such mass production requires multiple identicalmold tools that are typically installed on different moldingmachines—all of which are intended for making identical parts. Forexample, for the injection molding of a power brush's handle, which isdesigned to house a motor, a battery, and electronics, as well as tohave other functional attributes, the reliable uniformity and precisionamong the different molds, as well as the handle parts being made onthose molds, are of high importance.

Therefore, current molding processes, which require a high degree ofprecision with respect to dimensions of a part or parts being made,tolerate only limited size and shape variations among the parts beingmanufactured. For example, a typical current injection-molding processused in the production of power-toothbrush handles is particularlysensitive to length variations of the plastic components. During coolingthese components shrink, in absolute numbers, to a much greater extentin their lengthwise dimensions than they do in their dimensionsextending perpendicularly to the lengthwise dimensions—due to the factthat their lengthwise dimensions are several times greater than theirlargest dimension perpendicular to their lengthwise dimensions.

For example, for some typical embodiments of the toothbrush handles,e.g., those having an overall length in the range of about 120-200 mm,and more specifically in the range of about 140-180 mm, the currentmolding process allows for lengthwise tolerance of not greater than ±0.2mm in most of the successive molding operations. This may be difficultto maintain uniformly, particularly given the combination of all thefactors and concerns described herein above.

SUMMARY

The present invention resolves this problem of the required tighttolerances during successive molding operations, and particularlylengthwise molding tolerances of plastic parts being molded and/orovermolded, by providing a process for manufacturing multi-componentplastic structure that includes a novel functional element, atolerance-elimination element. Moreover, the present invention allowsmanufacturers to significantly relax lengthwise tolerances forshrinkable plastic parts, thereby providing a more reliable and stableprocess of manufacturing multi-component plastic housings comprisesthose parts. The present invention also allows one to have reducedlengthwise tolerances of the finished item, thereby providing for a moreconsistent uniformity of lengthwise dimensions among mass-producedmulti-component housings.

The tolerance-elimination element can be designed, structured, andconfigured to compensate for length deviations among plastic parts thatare molded and overmolded in successive steps of the process and thatare intended, in their solidified form, to be functionally and/orstructurally identical to one another. These deviations are primarilycaused, among other things, by differential shrinkage of the plasticmaterials used in the molding or overmolding steps. These deviations mayalso be caused by possible variation in the dimensions of the differentmold tools, molding conditions, and other relevant factors. Thus, thetolerance-elimination element allows one to have much greater lengthwisediscrepancies among the different plastic parts being molded, withoutnegatively affecting the desired uniformity among a plurality of thefinal products and the consistency of their dimensions.

The tolerance-elimination element can be located at either end of thehousing being made—and may include additional functional componentstherein, such as, e.g., engagement elements structured and configured tointerconnect and hold together different parts of the item being made.Such engagement elements may include, e.g., mechanical locks, threads,projections, depressions, and the like. While the tolerance-eliminationelement can be incorporated at any end or both ends of the item, thepresent disclosure will focus on embodiments in which thetolerance-elimination element is located at a “bottom” end of themulti-component housing.

The tolerance-elimination element can be overmolded with a finishingplastic material, such as, e.g., a soft-plastic material, that would atleast partially form an outer surface of the finished item. Such afinishing plastic material can be structured to cover thetolerance-elimination element either completely or partially, dependingon a particular design of the item being made.

In one aspect, the present disclosure is directed to a process formaking a multi-component hollow housing from a shrinkable plasticmaterial. The multi-component housing can comprise at least threeplastic materials. The finished housing has a top end, a bottom end, anda length therebetween that is parallel to a longitudinal axis of thehousing and extends between the top and bottom ends thereof. The processcomprises several steps.

A first plastic material can be injected into a first mold cavity havinga first-cavity length. A mold core can at least partially be disposed inthe first mold cavity. As the first plastic material solidifies, itshrinks lengthwise by a first absolute lengthwise shrinkage. Thesolidified first plastic material forms a first component, whichcomprises a generally tubular structure made of the first plasticmaterial. The first component has a first end and a second end oppositeto the first end and a first solidified length therebetween. The firstsolidified length of the shrunken first material is smaller than thefirst-cavity length.

Then the core, together with the first component disposed thereon, canbe positioned in a second mold cavity. The second mold cavity has asecond-cavity length that is greater than the first-cavity length by adistance greater than the first absolute lengthwise shrinkage of thefirst plastic material during solidification. A second plastic materialcan be injected into the second mold cavity and caused to solidify toform a second component made of the second plastic material and attachedto the first component. The first and second components joined togetherform an intermediate part.

The second mold cavity can be structured to cause at least a portion ofthe second plastic material, injected into the second mold cavity, toform a tolerance-elimination element that is longitudinally adjacent tothe first component at one of the first and second ends thereof. Thetolerance-elimination element has a proximal end adjacent to the firstcomponent, a distal end opposite to the proximal end, and a lengththerebetween, which length can be constant—or alternatively can vary.

In embodiments wherein the tolerance-elimination element has an unevenlength along its circumference, an average length can be calculated asan arithmetic mean of a maximal length and a minimal length of thetolerance-elimination element, the maximal and minimal lengths extendingparallel to the longitudinal axis and between the proximal and distalends of the tolerance-elimination element. In embodiments wherein thetolerance-elimination element has a constant length, this constantlength constitutes an average length of the tolerance-eliminationelement, as well as its maximal length and its minimal length.

As the second plastic material forming the tolerance-elimination elementsolidifies, it too shrinks lengthwise. But the absolute lengthwiseshrinkage of the second plastic material forming thetolerance-elimination element is at least ten times smaller than thefirst absolute lengthwise shrinkage of the first plastic material. Thesecond mold cavity can be structured so that the maximal length of thetolerance-elimination element adjacent to the first component is atleast ten times smaller than the first solidified length of the firstcomponent.

In a next step, the intermediate part, comprising the first and secondcomponent joined together, can be overmolded with a third plasticmaterial in a third mold cavity. A solidified third plastic materialforms a third component, made of the third plastic material and attachedto at least one of the first component and the second component. In theresulting multi-component housing, comprising at least the firstcomponent, the second component, and the third component, thetolerance-elimination element is at least partially overmolded by thethird plastic material, which forms at least a portion of an outersurface of the finished multi-component housing. Lastly, themulti-component housing can be removed from the core.

The second plastic material may be injected into the second mold cavityto form therein a first portion and a second portion, wherein the firstportion of the second plastic material at least partially overmolds thefirst component, and the second portion of the second plastic materialforms the tolerance-elimination element. In a further embodiment, boththe first portion and the second portion of the second plastic materialmay be formed with a single injection shot. Alternatively, the firstportion and the second portion of the second plastic material may beformed with two separate injection-molding shots, using two injectionnozzles.

The first plastic material, the second plastic material, and the thirdplastic material may differ from one another in at least onecharacteristic selected from the group consisting of color, opacity,porosity, and hardness. Alternatively, at least two of the first,second, and third plastic materials may be identical to one another. Inone embodiment, at least one of the first plastic material, the secondplastic material, and the third plastic material is a hard-plasticmaterial. In another embodiment, at least one of the first plasticmaterial, the second plastic material, and the third plastic material isa soft-plastic material.

In one particular embodiment, the first plastic material is a firsthard-plastic material, the second plastic material is a secondhard-plastic material different from the first hard-plastic material,and the third plastic material is a soft-plastic material. Embodimentsare contemplated in which the multi-component housing comprises morethan the three plastic materials. In one such embodiment, themulti-component housing may comprise, e.g., a first hard-plasticmaterial, a second hard-plastic material, a third soft-plastic material,and a fourth soft-plastic material, wherein the third and fourthsoft-plastic materials overmold different areas or portions of the firstand second hard-plastic materials. One of such areas or portions maycomprise, e.g., an ON/OFF button or switches or other control elements,which are conventionally located on the housings, particularly thosecomprising power tools, such as power toothbrushes.

In one embodiment, an outer surface of the tolerance-elimination elementis completely overmolded by the third plastic material so that thetolerance-elimination element does not form any part the finished item'souter surface. In another embodiment, the third material, whichcompletely overmolds the tolerance-elimination element's outer surface,extends beyond a distal end of the tolerance-elimination element so thatthere is a distance between the third material's edge and thetolerance-elimination element's distal end. The formed distance can befrom about 0.5 mm to about 3 mm.

In a further embodiment, the third plastic material may flow over asurface of the distal end of the tolerance-elimination element duringthe step of at least partially overmolding the combined intermediatepart with a third plastic material. This would result in the thirdmaterial at least partially overmolding the variable-ring distal end'ssurface. The surface of the distal end of the tolerance-eliminationelement can be perpendicular or inclined relative to the longitudinalaxis of the housing.

In a further embodiment, the process may comprise positioning a slidingstripper on a mold core. Such a sliding stripper may be structured andconfigured to accomplish at least two functions: to form a part of amolding cavity during one of the injection-molding steps; and to slidealong the core to remove or strip the finished item from the core. Thesliding stripper can be structured, e.g., as a single-piece sleeve.Alternatively, the stripper can comprise more than one parts joinedtogether on the mold core.

The stripper can be positioned at a distance from about 0.5 mm to about3 mm from the distal end of the tolerance-elimination element, so thatthe third plastic material being injected and advancing in the moldcavity along the longitudinal axis is stopped by the stripper at adesired distance from the distal end of the tolerance-eliminationelement. Thus the stripper, by touching the third plastic materialinside the mold cavity, can form an edge of the third plastic materialwhen the third plastic material extends beyond the distal end of thetolerance-elimination element. The stripper's surface can be profiled toform a desired shape of the third plastic material's edge. In a finalstep of the process, the stripper can be caused to slide along the coreto remove the multi-component housing from the core.

Depending on a particular embodiment of the housing being manufactured,the tolerance-elimination element can be shaped and sized to eliminateor greatly decrease size-related tolerances—particularly a lengthwisetolerance, related to the shrinkage of the plastic material during itscooling and solidification—that would otherwise be required for thepurposes discussed herein above. In one embodiment, thetolerance-elimination element comprises a ring-type structure having asubstantially even length along its circumference. The length of thetolerance-elimination element extends parallel to the longitudinal axis.Alternatively, the tolerance-elimination element can be beneficiallyshaped and sized to comprise a ring-type structure having uneven lengthalong its circumference. Such an embodiment may be particularly usefulin a multi-component housing having a relatively complex geometry.

In one embodiment, the tolerance-elimination element comprises aring-type structure having a minimal length Hmin of from about 1 mm toabout 20 mm and a maximal length Hmax of from about 10 mm to about 30mm. In another embodiment, the tolerance-elimination element comprises aring structure having an average length H of from about 3 mm to about 20mm and from about 5 mm to about 10 mm.

In one exemplary embodiment, the tolerance-elimination element,structured and configured to have an average length H of about 5 mm,allows the multi-component housing having an overall length L of about150 mm to have a very small lengthwise tolerance of less than 0.05 mm,and more specifically from about 0.01 mm to about 0.05 mm, or from about0.007% to about 0.033%, depending on the plastic material and theprocess. A comparable multi-component housing made of the identicalplastic materials—but lacking the tolerance-elimination element—wouldrequire a much greater lengthwise tolerance in order to accommodate theconcerns related to the plastic material's shrinkage resulting from itscooling and solidification, as is described herein above.

Thus, the lengthwise tolerance needed for the comparable multi-componenthousing not having the tolerance-elimination element is from about 0.3mm to about 1.5 mm in absolute numbers—or from about 0.2% to about 1.0%relative to the overall length of the comparable housing having anidentical length L of about 150 mm. That is so because in the housinglacking the tolerance-elimination element the entire length of thehousing, which shortens as a result of the shrinkage caused bysolidification of the plastic material, needs to be taken into accountfor the purposes of tolerance, while in the housing of the invention,equipped with the tolerance-elimination element, only thetolerance-elimination element, which is several times shorter than theentire housing, is ultimately responsible for the shrinkage affectingtolerance.

In another aspect, the disclosure is directed to a process for making amulti-component housing for a toothbrush handle. Such housing can have atop end, a bottom end, a longitudinal axis, and a length extendingparallel to the longitudinal axis and between the top and bottom ends.The housing can have several layers of plastic material, wherein some ofthe layers overmold one another, and wherein the plastic materials in atleast some of the layers differ from one another.

The process for making a multi-component housing for a toothbrush handlecomprises: injecting a first hard-plastic material into a first moldcavity having a core at least partially disposed therein, the first moldcavity having a first-cavity length; causing the first hard-plasticmaterial to solidify, whereby the first hard-plastic material shrinkslengthwise by a first absolute lengthwise shrinkage and whereby a firstcomponent is formed, the first component comprising a generally tubularstructure having a first end and a second end opposite to the first endand a first solidified length therebetween, wherein the first solidifiedlength is smaller than the first-cavity length; positioning the core,together with the first component disposed thereon, in a second moldcavity having a second-cavity length that is greater than thefirst-cavity length by a distance greater than the first absolutelengthwise shrinkage of the first hard-plastic material; injecting asecond hard-plastic material into the second mold cavity and causing thesecond hard-plastic material to solidify thereby forming a secondcomponent attached to the first component, the second componentcomprising a tolerance-elimination element that is longitudinallyadjacent to the first component at one of the first and second endsthereof; wherein the tolerance-elimination element has a proximal endadjacent to the first component, a distal end opposite to the proximalend, and an average length that is arithmetic mean of a maximal lengthand a minimal length of the tolerance-elimination element, the maximallength and the minimal length extending parallel to the longitudinalaxis and between the proximal and distal ends of thetolerance-elimination element, wherein the first solidified length ofthe first component is at least ten times greater than the maximallength of the tolerance-elimination element, and wherein an absolutelengthwise shrinkage of the second hard-plastic material forming thetolerance-elimination element is at least ten times smaller than thefirst absolute lengthwise shrinkage of the first hard-plastic material;at least partially overmolding the intermediate part with a soft-plasticmaterial in a third mold cavity to form a third component attached to atleast one of the first component and the second component, therebyforming the multi-component housing in which an outer surface of thetolerance-elimination element is at least partially overmolded by thesoft-plastic material, and wherein the soft-plastic material forms atleast a portion of an outer surface of the multi-component housing; andremoving the multi-component housing from the core.

The second hard-plastic material can be injected to form a first portionand a second portion, wherein the first portion at least partiallyovermolds the first component comprising the first hard-plasticmaterial, and the second portion forms the tolerance-elimination elementadjacent to one of the first component's opposite ends. Both the firstportion and the second portion of the second hard-plastic material canbe formed with a single injection shot.

In one embodiment, the step of at least partially overmolding thecombined intermediate part with a soft-plastic material results in thetolerance-elimination element being completely overmolded by the softplastic material, so that the tolerance-elimination element does notform any part the finished toothbrush handle's outer surface—and cannotbe seen under the surface of the soft-plastic material if the softplastic material is sufficiently opaque.

The process may further comprise a step of positioning a slidingstripper that forms a part of the third mold cavity on a mold core. Thesliding stripper can be positioned to abut the surface of thetolerance-elimination element. The sliding stripper can be positioned sothat it touches the soft-plastic material being injected when theinjected soft-plastic material is extending beyond the distal end of thetolerance-elimination element. By contacting the soft-plastic material,the surface of the sliding stripper facilitates the formation of an edgeof the soft-plastic material. The sliding stripper's surface thatcontacts the soft-plastic material can be configured to profiled theedge of the soft-plastic material in a desired manner. In oneembodiment, a distance of from about 0.5 mm to about 3 mm can be formedbetween the edge of the soft-plastic material in contact with at least aportion of the stripper and at least a portion of the distal end of thetolerance-elimination element. In a further embodiment, a surface of thedistal end of the tolerance-elimination element can be at leastpartially overmolded by the soft-plastic material. The surface of thedistal end of the tolerance-elimination element is oriented orthogonallyrelative to the longitudinal axis of the housing. As used herein, theterms “orthogonal,” “orthogonally,” and any variations thereof refer todimensions or orientations that are not substantially parallel to thelongitudinal axis—and that include those perpendicular or inclined (atgreater or lower than 90 degrees angles) relative to the longitudinalaxis of the housing. At the end of the process, the sliding stripper canmove the housing along the mold core thereby stripping the finishedhousing from the core. Depending on the process, one or more slidingstrippers can be utilized.

During cooling of the second hard-plastic material, thetolerance-elimination element shrinks, in absolute length, to a muchsmaller extent than the first and/or second materials would have shrunkin a comparable housing constructed without the tolerance-eliminationelement. This much smaller shrinkage of the tolerance-eliminationelement is due to the fact that the tolerance-elimination element ismuch shorter than the housing as a whole. Even though relative orproportional lengthwise shrinkage (as a percentage of the length) of thetolerance-elimination element on the one hand and the housing withoutthe tolerance-elimination element on the other hand can be similar oridentical, the absolute lengthwise shrinkage of thetolerance-elimination element is much lower than that of the entirehousing.

In one embodiment, the resulting multi-component housing for thetoothbrush handle has a lengthwise tolerance of from 0.01 mm to 0.05 mm.In another embodiment, the resulting multi-component housing for thetoothbrush handle has a lengthwise tolerance of from of from about0.006% to about 0.03% relative to the length L of the multi-componenthousing.

In one embodiment, after the second hard-plastic material hassolidified, the tolerance-elimination element has the longitudinalminimal length Hmin of from about 1 mm to about 20 mm. In anotherembodiment, after the second hard-plastic material has solidified, thetolerance-elimination element has the longitudinal minimal length Hminof from about 2 mm to about 15 mm. In a further embodiment, after thesecond hard-plastic material has solidified, the tolerance-eliminationelement has the longitudinal minimal length Hmin of from about 3 mm toabout 10 mm. The longitudinal maximal length Hmax of the solidifiedtolerance-elimination element can be from about 10 mm to about 30 mm.

The first hard-plastic material and the second hard-plastic material maydiffer from one another in at least one characteristic selected from thegroup consisting of color, opacity, porosity, and hardness. But anembodiment is contemplated, in which the first hard-plastic material andthe second hard-plastic material are identical. In one specificembodiment, at least one of the first hard-plastic material and thesecond hard-plastic material is transparent or translucent, and the softmaterial is opaque.

In a further aspect, the disclosure is directed to a multi-componenthousing comprising at least a first component, a second component, and athird component. The first component comprises a first plastic materialand has a first end and a second end opposite to the first end. Thesecond component comprises a second plastic material. The thirdcomponent comprises a third plastic material. The at least first,second, and third components are joined together to form a substantiallytubular structure having a longitudinal axis, a top end and a bottom endopposite to the top end, a length L parallel to the longitudinal axisand extending between the top end and the bottom end, and a maximalorthogonal dimension Dmax extending perpendicular to the longitudinalaxis. The length L of the housing is at least three times greater thanthe maximal orthogonal dimension Dmax extending perpendicular to thelongitudinal axis.

The housing includes at least one tolerance-elimination element made ofthe second plastic material and attached to one of the first and secondends of the first component along the longitudinal axis. Thetolerance-elimination element has a proximal end and a distal endopposite thereto. The proximal end is adjacent to at least one of thefirst and second ends of the first component. The tolerance-eliminationelement has an average length H, parallel to the longitudinal axis,extending between the proximal end and the distal end. The averagelength H is at least ten times less than the length L of the housing.The third component at least partially forms an outer surface of thehousing, so that the tolerance-elimination element is at least partiallyovermolded by the third plastic material.

As used herein, the term “maximal orthogonal dimension” of the housing(or any of its elements) refers to the housing's (or any of itselements') largest dimension measured substantially perpendicular to thelongitudinal axis of the housing. For example, in a housing structuredas a regular cylindrical tube the maximal orthogonal dimension is thehousing's outer diameter.

In another aspect, the disclosure is directed to a multi-componenthousing for a toothbrush handle. The multi-component housing for atoothbrush handle has a top end, a bottom end opposite to the top end,and a longitudinal axis therebetween. The housing also has a length L offrom about 120 mm to about 200 mm extending between the top and bottomends and a maximal orthogonal dimension Dmax extending perpendicular tothe longitudinal axis. The length L of the housing is at least threetimes greater than the maximal orthogonal dimension Dmax extendingperpendicular to the longitudinal axis.

The housing comprises at least a first component made of a firsthard-plastic material and having a first end and a second end oppositethereto, a second component made of a second hard-plastic material, anda third component made of a soft-plastic material. The first component,the second component, and the third component are integrally joinedtogether to form a generally tubular structure.

The housing includes at least one tolerance-elimination element made ofthe second plastic material and attached to one of the first and secondends of the first component along the longitudinal axis. Thetolerance-elimination element has a proximal end adjacent to the firstcomponent and a distal end opposite to the proximal end. Thetolerance-elimination element may be at least partially overmolded bythe soft-plastic material. The tolerance-elimination element has anaverage length H of from about 3 mm to about 20 mm extending parallel tothe longitudinal axis between the proximal end and the distal end of thetolerance-elimination element. The tolerance-elimination element causesthe housing to have a lengthwise tolerance of from about 0.006% to about0.03% relative to the length L of the housing.

In its further aspect, the disclosure is directed to a plurality ofmass-produced identical multi-component housings, as is described hereinabove, wherein the tolerance-elimination elements of the plurality ofmulti-component housings cause the individual housings to havelengthwise maximal dimension variations of the length L to be notgreater than 0.1 mm among the individual multi-component housings. Insome embodiments, the average length H of the tolerance-eliminationelements of the plurality of the mass-produced housings varies among atleast some of the tolerance-elimination elements by a lengthwisedimension that is at least ten times greater than the lengthwise maximaldimension variations of the length L among the individualmulti-component housings.

In another aspect, the disclosure is directed to a plurality ofmass-produced identical multi-component housings for toothbrush handles,as is described herein above, wherein the tolerance-elimination elementin each of the multi-component housings is structured to cause theindividual housing to have a lengthwise tolerance of from about 0.006%to about 0.03% relative to the length L of the housing. Formulti-component housings typically having a nominal overall length offrom about 120 mm to about 200 mm and constructed to form handles ofpower toothbrushes or other power tools, the multi-component housingsare expected to have a lengthwise tolerance of not greater than 0.05 mmin absolute numbers—and lengthwise maximal dimension variations of theoverall lengths among the individual multi-component housings areexpected to be not greater than 0.1 mm. In relative terms, themulti-component housings can have a lengthwise tolerance of from about0.006% to about 0.03% relative to the nominal overall length of themulti-component housing, and lengthwise maximal variations in length offrom about 0.012% to about 0.06% among the individual housings.

In its final aspect, the disclosure is directed to a power toothbrushcomprising a handle and a removable attachment having cleaning elementsthereon, wherein the handle comprises a multi-component housingdescribed herein and structured and configured to receive therein anelectric motor, a battery, and various drive components to power theremovable attachment. In one embodiment, the tolerance-eliminationelement has an interior surface that includes engagement elements formedtherein and structured to interconnect different parts of the powertoothbrush. Beneficially, the tolerance-elimination element can becompletely overmolded by the soft-plastic material so that thetolerance-elimination element does not form any part of the outersurface of the toothbrush handle and is not visible under the surface ofthe soft-plastic material if the soft-plastic material is opaque.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims which particularly pointout and distinctly claim the subject matter that is regarded as theinvention, the various embodiments will be better understood from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic plan view of an embodiment of a molding device anda process for making a multi-component housing that does not utilize atolerance-elimination element, the molding device including two moldingstations and one stripping station.

FIG. 2A is a schematic cross-sectional view of a first molding stationshown in FIG. 1, before a first plastic material has been injected intoa first mold cavity.

FIG. 2B is a schematic cross-sectional view of a first molding stationshown in FIG. 2A, after the first plastic material has been injectedinto the first mold cavity.

FIG. 3A is a schematic cross-sectional view of a second molding stationshown in FIG. 1 and having therein the first component disposed on themold core, before a second plastic material has been injected into asecond mold cavity to at least partially overmold the first component.

FIG. 3B is a schematic cross-sectional view of a second molding stationshown in FIG. 3A after the second plastic material has been injectedinto the second mold cavity.

FIG. 4 is a schematic cross-sectional view of a multi-component housingmade by a process illustrated in FIGS. 1-3B, wherein the housing hasbeen made without the tolerance-elimination element, and wherein thehousing's length is at least three times greater than the housing'smaximal orthogonal dimension extending perpendicular to the longitudinalaxis of the housing.

FIG. 5 is a schematic plan view of another embodiment of a moldingdevice and a process of the present disclosure for making amulti-component housing that comprises a tolerance-elimination element,wherein the molding device includes three molding stations and onestripping station.

FIG. 6 is a schematic cross-sectional view of a first molding stationshown in FIG. 5, and of a step of a process comprising injection-moldingof a first plastic material into a first mold cavity to form a firstcomponent.

FIG. 6A is a schematic cross-sectional view of the first moldingcomponent comprising a solidified first plastic material.

FIG. 7 is a schematic cross-sectional view of a second molding stationshown in FIG. 5, having the first component disposed therein, andshowing a subsequent step of the process, comprising overmolding thefirst component with a second plastic material to form a combinedintermediate part comprising the first and second component joinedtogether, wherein the second plastic material forms atolerance-elimination element adjacent to one of the ends of the firstcomponent.

FIG. 7A is a schematic cross-sectional view of another embodiment of asecond molding station shown in FIG. 5, having the first componentdisposed therein, and showing a subsequent step of the processcomprising overmolding the first component with a second plasticmaterial to form a combined intermediate part comprising the first andsecond component joined together, wherein the second plastic materialcomprises a first portion that at least partially overmolds the firstcomponent and a second portion that forms the tolerance-eliminationelement adjacent to one of the ends of the first component.

FIG. 7B is an enlarged cross-sectional view of the embodiment of thetolerance-elimination element shown in FIG. 7A.

FIG. 7C is a front view of the embodiment of the tolerance-eliminationelement shown in FIG. 7B, wherein the shown front view includes apartial cross-section showing grooves formed on an interior surfaces ofthe tolerance-elimination element.

FIG. 8 is a schematic cross-sectional view of a third molding stationshown in FIG. 5, having the intermediate part of FIG. 7 disposedtherein, and showing a subsequent step of the process, comprisingovermolding the intermediate part with a third plastic material to forma multi-component housing, wherein the third plastic material at leastpartially overmolds the tolerance-elimination element.

FIG. 8A is a schematic cross-sectional view of another exemplaryembodiment the third molding station shown in FIG. 5, having theintermediate part of FIG. 7A disposed therein, and showing a subsequentstep of the process, comprising overmolding the intermediate part with athird plastic material to form a multi-component housing, wherein thethird plastic material at least partially overmolds thetolerance-elimination element, and wherein the multi-component housinghas a length that is at least three times greater than the housing'smaximal orthogonal dimension.

FIG. 8B is an enlarged portion of the cross-section shown in FIG. 8 andshowing a fragmental view 8B, wherein the third plastic materialcompletely overmolds the outer surface of the tolerance-eliminationelement and extends beyond a distant end thereof.

FIG. 8C is an enlarged portion of the cross-section similar to thatshown in FIG. 8, and showing an embodiment in which thetolerance-elimination element has an undercut.

FIG. 9 is a schematic cross-sectional view of another embodiment of theprocess, showing the second molding station having therein the firstcomponent and a molten second material adjacent to the first component'send and comprising the tolerance-elimination element being formed,wherein the latter is configured to compensate for a lengthwiseshrinkage of the first plastic material forming the first component.(The injection nozzle is not shown in FIG. 9 for convenience.)

FIG. 9A is a schematic cross-sectional view of the embodiment of theprocess shown in FIG. 9, and showing the third molding station, whereinthe first component and the tolerance-elimination element made of thesecond material attached to the first component are being overmolded bythe third plastic material to form a multi-component housing, whereinthe length of the multi-component housing is at least three timesgreater than the maximal orthogonal dimension of the housing.

FIG. 9B is an enlarged fragmental view of the cross-section shown inFIG. 9A and showing a the third plastic material completely overmoldingthe outer surface of the tolerance-elimination element and extendingbeyond a distant end thereof to at least partially cover a surface ofthe distal end of the tolerance-elimination element.

FIG. 9C is an enlarged cross-sectional view of an embodiment of thetolerance-elimination element shown in FIG. 9A.

FIG. 9D is a front view of the tolerance-elimination element shown inFIG. 9C.

FIG. 10A is a schematic cross-sectional view of an exemplary embodimentof a stripper that can be part of the mold tool of the third moldstation.

FIG. 10B is a front view of the stripper shown in FIG. 10A.

FIG. 11A is a schematic cross-sectional view of another exemplaryembodiment of a stripper that can be part of the mold tool of the thirdmold station.

FIG. 11B is a front view of the stripper shown in FIG. 11A.

FIG. 12A is a schematic cross-sectional view of yet another exemplaryembodiment of a stripper that can be part of the mold tool of the thirdmold station.

FIG. 12B is a front view of the stripper shown in FIG. 12A.

FIG. 13A is a schematic cross-sectional view of an exemplary embodimentof a stripper comprising multiple parts.

FIG. 13B is a front view of the stripper shown in FIG. 13A.

FIG. 14 is a schematic cross-sectional view of a first exemplaryembodiment of the tolerance-elimination device.

FIG. 15 is a schematic cross-sectional view of a second exemplaryembodiment of the tolerance-elimination device.

FIG. 16 is a schematic cross-sectional view of a third exemplaryembodiment of the tolerance-elimination device.

FIG. 17 is a schematic cross-sectional view of a fourth exemplaryembodiment of the tolerance-elimination device.

FIG. 18 is a schematic cross-sectional view of a fifth exemplaryembodiment of the tolerance-elimination device.

FIG. 19 is a schematic perspective view of an embodiment of a partiallymade handle of a toothbrush, comprising a first component made of afirst plastic material.

FIG. 20 is a schematic perspective view of the embodiment shown in FIG.14, comprising the first component made of the first plastic material, asecond component made of a second plastic material, and including atolerance-elimination element made of the second plastic material.

FIG. 21 is a schematic perspective view of the embodiment shown in FIGS.14 and 15, and comprising the first component made of the first plasticmaterial, the second component made of the second plastic material, anda third component made of a third plastic material, wherein the thirdplastic material completely covers an outside surface of thetolerance-elimination element.

FIG. 22 is a schematic perspective view of an embodiment of a toothbrushhaving a handle formed by a multi-component housing comprising atolerance-elimination element.

DETAILED DESCRIPTION

The following description does not attempt to list every possibleembodiment of the invention because that would be impractical if notimpossible. This disclosure, therefore, is to be construed as exemplary,that is, any feature, characteristic, structure, component, or stepdescribed herein can be combined with or substituted for, in whole or inpart, any other feature, characteristic, structure, component, or stepdescribed herein. It should also be understood that the relative scaleof some elements shown in the drawings may not be exact, i.e., athickness of plastic components shown in the several exemplaryembodiments is purposefully exaggerated for the purposes ofillustration.

An exemplary molding device, and its components, for manufacturingmulti-component housing 100, or a plurality of multi-component housings100, are variously shown in FIGS. 1-9. FIGS. 1-3B schematically show anembodiment of an exemplary process, wherein the multi-component housing(shown in FIG. 4) is manufactured without utilizing atolerance-elimination element. FIGS. 5-9B schematically show embodimentsof an exemplary process of the disclosure, wherein variousmulti-component housings (examples of which are shown in FIGS. 7A, 8,8A, 9A, and 19-21) can be manufactured with a tolerance-eliminationelement.

The multi-component housing 100 comprises an essentially hollowstructure, manufactured by step-by-step injection molding. Theinjection-molding process uses different mold cavities and typically asingle mold core that can be transferred, together with the plasticstructure being made, from one mold cavity to another. The core isstructured and configured to be at least partially located inside themold cavities during the various steps of the process. Hence, one end ofthe core can be covered by the plastic material being injected into amold cavity—and eventually by the hollow part being made, while theother end of the core is not covered by eth plastic material. The end ofthe core that is located inside the mold cavities and that is coveredwith the plastic material is termed herein a first end of the core; andthe opposite and is a second end of the core.

The molding device, a plan view of which is schematically shown in FIGS.1 and 5, may comprise two or more molding stations. In an exemplaryembodiment of the process shown in FIG. 1, the molding device comprisestwo molding stations 1, 2 and one stripping station 3. In an exemplaryembodiment of the process of the invention shown in FIG. 4, the moldingdevice comprises three molding stations 1, 2, 3 and one strippingstation 4. Each molding station has a mold cavity configured to form acertain portion of the hosing being made.

These successive portions may comprise layers, partial layers, andlocalized plastic parts made of various plastic materials formed in thesuccessive molding steps. The layers and parts of the housing being madethat have already been injected and formed on the core can betransferred from one molding station to another, i.e., by moving thecore from one station to the next one. To this end, theinjection-molding stations may be arranged adjacent to one another,e.g., in a linear manufacturing line (not shown), wherein the core canbe conventionally transferred, from station to station, from thebeginning of the manufacturing line to the end thereof.

Alternatively, the molding stations may be arranged along a circularpath, as is schematically shown in FIGS. 1 and 5. The stations may bearranged, e.g., along a circle or a rectangle, and the core can betransferred from one station to another by rotation. The degree of asingle-step rotation can be chosen depending on the number of moldingstations arranged around a circular or rectangular path. Thus, e.g., asingle-step rotation of 90° can be naturally used in the molding devicecomprising four stations arranged equiangularly from one another (FIGS.1 and 5).

After the molding process is complete, the hollow housing, stilldisposed on the core, can be removed therefrom. A sliding stripper,located at the second end of the core, can be structured and configuredto accomplish this task of removing, or stripping the finished housingfrom the core. To this end, the stripper can be moved along the core inthe direction of the first end of the core.

The stripper can be also structured and configured to form a part of atleast one of the mold cavities during the injection-molding processoccurring in that cavity. Thus, the stripper can slide along thecore—and can be positioned in more than one place on the core. In oneembodiment, the stripper can travel along the core to be located, e.g.,in three different positions on the core.

The stripper may be structured as a single-part complete or partialsleeve or ring. Alternatively, the stripper can be structured tocomprise more than one part. The stripper may be made of any suitableheat-resistant material capable of withstanding the temperatures ofhot-melted plastic materials. One non-limiting example of such aheat-resistant material is stainless steel.

It should be understood that while the disclosure refers mostly to asingle stripper, more than one stripper could be arranged on the core,depending on the process and equipment. For example, two different,similar, or identical strippers can be located at opposite sides of thecore.

Since the stripper can comprise a part of a mold cavity, differentstrippers can be used in different molding operations or in differentmold cavities to form different elements of the housing beingmanufactured. If two or more strippers are used in the molding devicedisclosed herein, all strippers can be movable and all can be structuredto accomplish the functions disclosed herein.

The stripper can be arranged on the core in at least three differentpositions: passive position, molding position, and demolding orstripping position. In a passive position, the stripper is arranged nearthe second end of the core, outside the mold cavity. In a moldingposition, the stripper forms a part of the mold. In other words, whenthe mold is closed, a “molding” surface of a first end of the stripperfacing the mold comprises a part of a surface of the mold cavity thatcontacts the plastic material injected into the mold cavity. To put itanother way, the stripper in the molding position is arranged on thecore to close or seal the mold cavity at one end. Because the first endof the stripper forms a part of the mold cavity's surface, the shape ofthe stripper's first end can be profiled to form a desired surface,which would be contacted by the plastic material to form a mirrorsurface of the surface of the stripper's first end.

The stripper's molding surface may include, e.g., various inclinedsurfaces, recesses, projections, and the like. Thus, complex parts, suchas, e.g., undercuts and inclined depressions, can be formed relativelyeasily during the injection-molding process. If more than one stripperis used, the strippers may have differently shaped first ends, whichwould allow one to form differently shaped parts of the housing beingmade. Also, multiple strippers may be located at their molding positionsat different locations on the core in order, so that different parts ofthe housing being made could be easily formed. Of course, if all of themultiple strippers have identical first ends that are arranged atidentical molding positions, a plurality of identically shaped parts canbe formed for the housing being made.

FIGS. 10A-13B show several exemplary designs of a stripper 35. While allthe exemplary strippers shown are configured for a cylindrical moldcore, it should be appreciated that any suitable shapes of thestripper's inner orifice designed to fit a corresponding core can behad. An embodiment of the stripper 35 shown in FIGS. 10A and 10B has aninner diameter D1 and a first end 31 that is planar and substantiallyperpendicular to the longitudinal axis X of the core (not shown). Anembodiment of the stripper 35 shown in FIGS. 11A and 11B has first end31 that is planar and inclined relative to the longitudinal axis X ofthe core (not shown). An embodiment of the stripper 35 shown in FIGS.12A and 12B has a first end 31 that is concave and inclined. Anembodiment of the stripper 35 shown in FIGS. 13A and 13B (shown apartand disengaged from a core 15 for illustration) comprises two parts, afirst part 36 and a second part 37. The first part 36 has a flat firstend 31 a that is substantially perpendicular to the longitudinal axis Xof the core 15, while the second part 37 has a first end 31 b that isconvexly shaped and is inclined relative to the longitudinal axis X ofthe core 15.

In a demolding or stripping position, the stripper is positioned on thecore to remove the finished item. The demolding position is the positionthat is nearest to the first end of the core. In other words, thedistance from the first end of the core to the first end of the stripperin the demolding position is smaller than the size of the hollow part.In particular, the distance is smaller enough to allow the stripper tostrip the housing from the core. If more than one stripper is used inthe process, the demolding position of multiple strippers relative tothe core may be identical or different. If, e.g., the injected hollowpart is asymmetrical or irregular, the demolding positions of thestrippers may be adapted to the dimension of the housing.

As is known in the art, each of the mold cavities of the molding devicemay be formed by multiple parts. The mold cavity may, e.g., be formed bya first mold half and a second mold half. As used herein, a “mold half”means any part that forms a limiting surface or a part thereof of themold cavity. In that sense, the mold “half” may greater or smaller thanthe mold's real physical half. In addition, the volume of the moldcavity is also limited by the core, which is located at least partiallyin the mold cavity. The plastic material can be injected into the moldcavity by one or several injection nozzles, as is known in the art.

FIG. 1 shows an exemplary embodiment of a molding device comprising afirst molding station 1, a second molding station 2, and a demolding orstripping station 3. The first molding station 1 is shown with a firstplastic material 41 a already injected onto a core 15 in a first moldcavity 10 a of a first mold 10, to form a first plastic component 41. Amovable stripper 35 is arranged on the core 15 in a passive position PPoutside the first mold 10.

The second molding station 2 is shown, likewise, after a second plasticmaterial 42 a has been injected into a mold cavity 20 a of a second mold20, to form a second plastic component 42 that at least partially coversor “overmolds” the first plastic component 41. The stripper 35 has nowmoved on the core 15 to be in its molding position MP, whereby a“molding” surface of the first end 31 of the stripper 35 forms a part ofthe interior surface of the mold cavity 20 a.

At the demolding or stripping station 3, the stripper 35 removes, orstrips a finished housing 40 from the core 15. Here, the stripper 35 isarranged on the core 15 in its demolding position DP, whereby thestripper 35, being in contact with the housing 40, travels towards thefirst end of the core 15, thereby removing the housing 40 from the core15. An arrow “Y” indicates the stripper's movement along the core 15 asthe stripper removes the housing 40 therefrom. The finished housing 40comprises a substantially hollow structure composed by a first component41 at least partially overmolded by a second component 42.

At a fourth position 4, the movable stripper 35 rests in its passiveposition PP on the core 15. From here, the core 15 can be transferred tothe first station by a 90-degree rotational step, and theinjection-molding process can be repeated.

FIG. 2A shows an enlarged cross-sectional view of the first moldingstation 1 before the first plastic material 41 a has been injectedthereto. The first mold 10 comprises a first mold half 11 and a secondmold half 12, which are arranged to form the first mold cavity 10 a. Afirst injection nozzle 19 is shown as passing through the second moldhalf 12 into the first mold cavity 10 a. The core 15 is arranged withits first end 16 disposed inside the first mold cavity 10 a. The slidingstripper 35, in contact with a surface 17 of the core 15, is arranged inits passive position PP outside the first mold cavity 10 a.

FIG. 2B shows an enlarged cross-sectional view of the first moldingstation 1 after a first plastic material 41 a, in its melted form, hasbeen injected, through the nozzle 19, into the first mold cavity 10 a,to form a first plastic component 41 therein. The stripper 35 rests inits passive position PP outside the mold 10.

FIG. 3A shows an enlarged cross-sectional view of the second moldingstation 2 before the second plastic material has been injected thereto.The second mold 20 comprises a first mold half 21 and a second mold half22, which are arranged to form the second mold cavity 20 a. A secondinjection nozzle 29 is shown as passing through the second mold half 22into the second mold cavity 20 a. The core 15, carrying the firstplastic portion 41, made of the first plastic material 41 a, is arrangedwith its first end 16 inside the second mold cavity 20 a. The slidingstripper 35 is moved into its molding position MP, wherein the moldingsurface of the stripper's first end 31 forms a part of the mold 20. Inthe exemplary embodiment of the stripper 35 shown in FIGS. 3A and 3B,the surface of the first end 31 of the stripper 35 is inclined, but oneskilled in the art would appreciate that the first end 31 of thestripper 35 can be shaped in any desired manner.

FIG. 3B shows an enlarged cross-sectional view of the second moldingstation 2 after the second plastic material 42 a has been injectedthereto through the second injection nozzle 29, to form the secondplastic component 42 joined to the first plastic component 41. Dependingon the design of the multi-component housing being made, the secondplastic material 42 a can be injected to fully or partially overmold thefirst component's outer surface, which is not in contact with the core15. In FIG. 3B, the stripper 35, arranged in its molding position MPadjacent to the second mold 20, forms a part of the second mold cavity20 a. The inclined surface of the stripper's first end 31 in contactwith the second plastic material 42 a forms a corresponding undercut 33in the second portion 42 of a resulting multi-component housing 40 (FIG.4), comprising the first component 41 and the second component 42.

FIG. 5 shows an embodiment of a molding device similar to that shown inFIGS. 1-3B but illustrating a novel process of the invention, whereinthe tolerance-elimination element is utilized in the construction of themulti-component housing 100 being made. The movable stripper 35, in thisexemplary embodiment, comprises at least two parts, or “halves”: a firststripper part 36 and a second stripper part 37, which can be structuredto move either in unison or independently from one another, depending onthe process. This type of the stripper 35 is illustrated in more detailin FIGS. 13A and 13B.

A first molding station 1 is shown in FIGS. 5 and 6 after the firstplastic material 41 a has been injected onto the core 15 in the firstmold cavity 10 a of the first mold 10. The first mold cavity 10 a has afirst-cavity length L1 (FIG. 6). During cooling and solidification, thefirst plastic material 41 a shrinks, as is explained herein above. Theresulting first component 41, comprising the solidified first plasticmaterial 41 a, has a first solidified length LS1 that is smaller thanthe first-cavity length L1 by an amount of the longitudinal shrinkage S(FIG. 6A). The first component 41 may have any suitable wall thickness,which may be constant throughout the first component 41—or alternativelymay vary. In one exemplary embodiment, particularly suitable for amulti-component housing designed for a toothbrush handle, the firstcomponent 41 may have a thickness of from about 0.5 mm to about 2.5 mm,and more specifically from about 0.9 mm to about 1.9 mm.

For example, a plastic material comprising polypropylene and having alength of about 150 mm and an average thickness of about 0.7-2.4 mm inits liquid state is expected to lose, during solidification, from about0.3 mm to about 1.5 mm in absolute numbers (depending on the processconditions, the average being about 0.6 mm)—or from about 0.2% to about1.0% of its original length. Naturally, the first component 41 in thisinstance will have the average solidified length LS1=150.0 mm-0.6mm=149.4 mm. At the upper limit of the shrinkage range, the firstcomponent 41 will have the average solidified length LS1 of about 148.5mm (150.0 mm−1.5 mm=148.5 mm). To eliminate or significantly minimizethe lengthwise tolerance caused by such a substantial shrinkage, theprocess of the disclosure utilizes a tolerance-elimination element thatis designed to at least partially absorb, or even eliminate altogether,length deviations affecting solidified plastic components caused by theshrinkage of the plastic material comprising those components.

A second molding station 2 is shown in FIGS. 5 and 7 after the secondplastic material 42 a has been injected into the second mold cavity 20 aof the second mold 20, to form a combined intermediate part 45,comprising the first component 41 and the second component 42 joinedtogether. The second component 42 may have any suitable wall thickness,which may be either constant or vary throughout the second component 42.In one exemplary embodiment, particularly suitable for a multi-componenthousing designed for a toothbrush handle, the second component 42 mayhave a thickness of from about 0.5 mm to about 2.5 mm, and morespecifically from about 1.0 mm to about 1.6 mm.

The intermediate part 45, likewise, may have any suitable, constant orvarying, wall thickness. One skilled in the art will understand that inembodiments in which the intermediate part 45 is formed by one or moreplastic materials overmolding one or more components, i.e., embodimentscomprising two or more layers of plastic materials/components in atleast some portions of the housing, the resulting thickness of thehousing in those portions will comprise a sum of thicknesses of therelevant layers of the plastic materials. In one exemplary embodiment,particularly suitable for a multi-component housing designed for atoothbrush handle, the first component 42 may have a thickness of fromabout 0.8 mm to about 2.5 mm, and more specifically from about 1.0 mm toabout 1.2 mm.

The second component 42 includes the tolerance-elimination element 50that is integrally attached to one of the ends of the first component41. The molten second plastic material 42 a being injected into thesecond mold cavity 20 a flows into, and at least partially occupies, thespace created by the shrinkage of the first material 41 a. The secondplastic material 42 a contacts the first component 41 and integrallyattaches thereto. Thus, the second material 42 a that occupies the“shrinkage” space absorbs the shrinkage. When the second plasticmaterial 42 a solidifies to form the tolerance-elimination element 50,it also experiences some degree of shrinkage. However, because thetolerance-elimination element 50 is many times shorter than the firstcomponent 41, the lengthwise shrinkage affecting thetolerance-elimination element 50 is many times less that the lengthwiseshrinkage of the first plastic material 41 a.

In the context of mass production of a plurality of multi-componentidentical housings, the average length H, the maximal length Hmax, andthe minimal length Hmin of individual tolerance-elimination elementswill vary, depending on the individual amounts of the first material'sshrinkage absorbed by the individual tolerance-elimination elements.Thus, the individual tolerance-elimination elements in the plurality offinished mass-produced multi-component housings may differ from oneanother lengthwise to a much greater extent than their respectivelengthwise shrinkage would otherwise cause.

In the finished housings, however, the length variations will beprimarily defined by the lengthwise shrinkage differential among theindividual tolerance-elimination elements. This lengthwise shrinkagedifferential is at least ten times less than that among the individualfirst components, assuming comparable shrinkage rate between the firstand second plastic materials and at least the 10× difference in lengthbetween the first component and the tolerance-elimination element. Thus,in the plurality of mass-produces multi-component housings the averagelength H, the maximal length Hmax, and the minimal length Hmin will varyamong at least some of the tolerance-elimination elements by alengthwise dimension that is at least ten times greater than thelengthwise maximal dimension variations of the length L among theindividual multi-component housings in the plurality.

Assuming that the rates of shrinkage of first material 41 a (comprisingthe first component 41) and the second material 42 a (comprising thetolerance-elimination element 50) are generally comparable, the absoluteshrinkage differential between the first component 41 and thetolerance-elimination element 50 can be expected to be approximatelyproportional to the length differential between the two. If, e.g., thefirst component 41 were about ten times longer than thetolerance-elimination element 50, the lengthwise shrinkage of the formerwould be expected to be about ten times greater than that of the latter.

In addition, at least in some embodiments, a plastic material having arate of shrinkage proportionally smaller than that of the first plasticmaterial 41 a can be selected as the second plastic material 42 a, whichforms the tolerance-elimination element 50. In such instances, theabsolute lengthwise shrinkage of the tolerance-elimination element 50would be even smaller than that of a material having a shrinkage rateproportionally comparable with that of the first plastic material 41 a.Such a second plastic material 42 a, having a proportionally lower rateof shrinkage, might not be suitable or desirable for formingsubstantially larger or functionally different portion or portions ofthe housing because of one or more undesirable properties that may beinherent in such a low-shrinkage material. Such a material, however, maybe acceptable for the purposes of forming a relatively short part of thehousing comprising the tolerance-elimination element 50, particularly ifthe latter will not be visible in the finished housing, and will not beotherwise affecting its appearance and quality.

FIG. 7A schematically illustrates another embodiment of a second moldingstation 20 and the step of the process of the invention. Here, theintermediate part 45, comprising the first and second components 41, 42joined together, includes a first portion 421 and a second portion 422of the second plastic material 42 a (or the second plastic component42). The first portion 421 at least partially overmolds the firstcomponent 41 and the second portion 422 forms the tolerance-eliminationelement 50 adjacent to one of the ends of the first component 41. Itshould be understood that the terms “first portion 421” and “secondportion 422” are used in the present context conventionally, for thepurposes of illustration; in some embodiments, such as, e.g., the oneshown in FIG. 7A, there may be no well-defined, exact boundary or borderseparating the first portion 421 from the second portion 422, and thesecond component 42 as a whole can be a single element in which thefirst and second portions 421, 422 are integrally connected.

In the exemplary embodiment of FIG. 7A, each of the first portion 421and the second portion 422 of the second plastic material 42 a is shownas being injected primarily via a separate injection nozzle: a nozzle 29a injecting primarily the first portion 421 and a nozzle 29 b injectingprimarily the second portion 422. But it should be appreciated that inother possible embodiments, the two portions 421, 422 of the secondplastic material 42 a can be injected via a single injection nozzleand/or with a single injection shot. All of these embodiments are withinthe scope of this invention.

One embodiment of an exemplary tolerance-elimination element 50 isschematically shown in FIGS. 7B and 7C. The tolerance-eliminationelement 50 shown comprises a ring-type structure having a proximal end51 and a distal end 52 opposite to the proximal end 51. In the mold 20,the proximal end 51 is adjacent to one of the ends of the firstcomponent 41. The shape of interior walls 55 of thetolerance-elimination element 50 reflects the shape of a portion of themold core 15 on which the tolerance-elimination element 50 has beenformed; and the shape of exterior walls of the tolerance-eliminationelement 50 reflects the shape of a portion of the second mold cavity 20a in which the tolerance-elimination element 50 has been formed.

Therefore, if the tolerance-elimination element 50 needs to bestructured to have additional functional attributes, such as, e.g., afastening means and the like, which can be used for attaching thehousing to another element of an item of which the housing is designedto be a part of, then the relevant portions of the core 15 and/or themold cavity 20 a need to be profiled accordingly. The exemplaryembodiment of the tolerance-elimination element 50 shown in FIGS. 7B and7C has two mutually opposite grooves or undercuts 59, formed in theinterior walls 55.

While the tolerance-elimination element 50 shown in FIGS. 7A and 7B hasan essentially symmetrical (relative to an imaginary vertical axis)front face (FIG. 7C), comprising the proximal end 51, one skilled in theart would appreciate that the shape of the tolerance-elimination elementis largely dictated by the shape of the multi-component housing beingmade and other considerations described herein. Thus, any suitable shapeof the tolerance-elimination element is contemplated by this invention.

Such shapes may include circular, rectangular, triangular,multi-angular, elliptical, oval, et cetera geometrical shapes of anydesired and suitable proportions and combination thereof, as well assymmetrical, asymmetrical, and irregular shapes. In an exemplaryembodiment shown in FIGS. 9C and 9B, the tolerance-elimination element50 comprises an essentially symmetrical ring structure having a constantlength H throughout its circumference. In such an instance, it can besaid that the maximal length Hmax, minimal length Hmin and the averagelength H are equal.

At the same time, the tolerance-elimination element 50 shown in FIGS. 7Band 7C has an uneven length, ranging from a minimal length Hmin to amaximal length Hmax. In some embodiments, an average length H of thetolerance-elimination element having more than one length can becalculated as an arithmetic mean of the Hmax and Hmin, i.e.,H=½(Hmin+Hmax). While a gradual change of length is shown in theembodiment of FIGS. 7B and 7C, it is contemplated that various otherembodiments of the tolerance-elimination element 50 may have discreteand/or otherwise irregular or convoluted changes of the lengththroughout the circumference of the tolerance-elimination element 50. Asused herein, the term “circumference” refers to the enclosing boundaryof a curved geometric figure, which may comprises, in whole or in part,any shape, not limited to a circle.

As is explained herein, the shape of the tolerance-elimination elementis principally dictated by the shape of the multi-component housingbeing made. FIG. 17 illustrates one exemplary embodiment of thetolerance-elimination element 50 having such non-gradual change of itslength, from Hmin to Hmax. Likewise, while the embodiment of FIGS. 7B,7C illustrate the tolerance-elimination element 50 in which the minimallength Hmin is directly opposite to the maximal length Hmax, i.e., theminimal length Hmin and the maximal length Hmax are disposed at 180degrees relative to one another, embodiments are contemplated in whichthe minimal and maximal lengths Hmin, Hmax are not directly opposite toone another—but instead are located on the circumference of thetolerance-elimination element at an angle that is less or greater than180 degrees relative to one another, as is shown in an exemplaryembodiment of FIG. 18.

In FIG. 8, a third molding station 30 is shown after the third plasticmaterial 43 a has been injected thereinto to at least partially overmoldthe intermediate part 45, including the tolerance-elimination element50, formed by the second plastic material 42 a. A movable stripper 35 ais arranged on the core 15 in its molding position, to form a part ofthe third mold 30. That is, a surface of the first end of the stripper35 a forms a portion of the third mold cavity's surface intended tocontact the third plastic material 43 a being injected into the thirdmold cavity 30 a. While a stripper 35 a, different from the stripper 35,is shown in this exemplary embodiment, one skilled in the art wouldappreciate that the single stripper 35 can be used throughout theprocess. Utilization of a single stripper may be particularly beneficialfor those embodiments of the process in which the stripper is connectedto, or form a part of, an index plate.

FIG. 8A shows another exemplary embodiment the third molding station 30having the intermediate part 45 disposed therein and showing the step ofovermolding the intermediate part 45 with a third plastic material 43 a.The movable stripper 35 a is arranged on the core 15 in its moldingposition, to form a part of the third mold 30. In this embodiment thethird material 43 a covers the intermediate part 45 in a patterndifferent from the overmolding pattern shown in FIG. 8. Also, in thisexemplary embodiment, the third material 43 a is injected into the thirdmold 30 through two separate injection nozzles, 39 a and 39 b, disposedat opposite sides of the third mold.

FIG. 8B shows an enlarged view of a fragment of the cross-section shownin FIG. 8A, to illustrate a manner in which the third plastic material43 a can be caused to completely overmold the outer surface of thetolerance-elimination element 50—and even extend beyond a distant end 52thereof, into a touch-up area 60. The surface of the first end 31 of thestripper 35 b stops the advance of the molten third plastic material 43a. A similar fragment, in the context of another embodiment, is shown inFIG. 9B.

FIG. 8C shows an enlarged fragmental view similar to the one shown inFIG. 8, but showing a further embodiment of the tolerance-eliminationelement 50. In the embodiment of FIG. 8C, the tolerance-eliminationelement is constructed to have an undercut 59. For the purposes ofillustration, the undercut 59 is shown only on one side of thetolerance-elimination element 50, but embodiments are contemplated inwhich two or more undercuts can be had on the tolerance-eliminationelement 50. Also, an embodiment is contemplated in which an undercutextends to the full circumference of the tolerance-elimination element,although such a configuration would likely require a forced demolding.In one specific embodiment, particularly suited for a toothbrushhousing, the tolerance-elimination element 50 can have two undercuts 59(FIGS. 20, 21)—for the fixation of the bottom closure. Such undercutscan be made, e.g., by utilizing a slider in the core (not shown).

Relative dimensions of all cooperating parts, such as the shape anddepth of the third mold cavity, the size and shape of thetolerance-elimination element 50, the shape and position of the firstend 31 of the stripper 35 b, and the like elements, can be beneficiallydesigned to allow the third plastic material 43 a to slightly extendbeyond the distal end of the tolerance-elimination element, comprisingan edge of the intermediate part 45, to form a touch-up portion orportions 43 b disposed between a portion of the first end 31 of thestripper 35 a and a portion of the distal end 52 of thetolerance-elimination element 50. The tolerance-elimination element 50is beneficial as the intermediate part has low longitudinal tolerancesand thus compression of the intermediate part or flashes duringovermolding are avoided. Embodiments in which the third plastic material43 a does not extend beyond the distal end 52 of thetolerance-elimination element 50 are also contemplated. In suchembodiments, the third plastic material 43 a can flush with the distalend 52 of the tolerance-elimination element 50.

If the first end 31 does not touch the tolerance-elimination element 50(FIG. 9B), a touch-up distance TD can be formed between an edge of thethird plastic material 43 a in contact with the stripper's first end 31and the distal end 52 of the tolerance-elimination element 50. In oneembodiment, the touch-up distance can be from about 0.5 mm to about 3mm. In another embodiment, the touch-up distance TD can from about 1 mmto about 2 mm. In a further embodiment, the touch-up distance can be assmall as between about 0.1 mm and about 0.5 mm.

FIG. 9 schematically shows another embodiment of the multi-componenthousing and the process of the disclosure. A liquid second material 42 ais injected into the second mold cavity 20 a of the second mold 20 inthe location adjacent to the end of the solidified first component 41made of the first plastic material 41 a. (An injection nozzle is notshown for convenience.) The first plastic material 41 a has shrunkduring solidification so that the solidified first component 41 has a“shrunken” length LS1. Due to the shrinkage of the first plasticmaterial 41 a, the length LS1 of the first component 41 is smaller thanthe length of the first mold cavity 10 that was filled with the liquidfirst plastic material 41 a during a previous process step (not shown).The injected second material 42 a fills the second mold cavity 20 a,including a space “vacated” by the first plastic material 41 a as aresult of the shrinkage of the first plastic material 41 a, thereby“eliminating” the shrinkage affecting the solidified first plasticcomponent 41.

When the second material 42 a solidifies and attaches to the firstcomponent 41, the tolerance-elimination element 50 is formed. Due to thesignificant difference between the length L1 of the liquid first plasticmaterial 41 a and a length LT1 (FIG. 9) of the liquid second plasticmaterial 42 a forming the tolerance-elimination element 50, the absolutelengthwise shrinkage of the second plastic material 42 a forming thetolerance-elimination element 50 is significantly smaller than theabsolute lengthwise shrinkage of the first plastic material 41 a formingthe first component 41. Yet, because the second material 42 a “absorbs”the existing lengthwise shrinkage of the first plastic material 41 amaterialized in the first component 41, and because the absolutelengthwise shrinkage of the intermediate part 45 will now be defined bythe absolute shrinkage of the second plastic material 42 a forming thetolerance-elimination element 50, the overall absolute lengthwiseshrinkage experienced by the intermediate part 45 will also besignificantly smaller than the absolute shrinkage experienced by thefirst component 41.

The length L2 of the second mold cavity 20 a is greater than the lengthof the first mold cavity 10 a by a distance that allows for theformation of a desired tolerance-elimination element. This distance canbe calculated based on several principal considerations. The differencebetween the length L2 of the second mold cavity 20 a and the length L1of the first mold cavity 10 a should be greater than the expected amountof the shrinkage of the first material 41 a. In addition, the differencebetween the length L2 of the second mold cavity 20 a and the length L1of the first mold cavity 10 a should be sufficient for the formation ofthe tolerance-elimination element 50 having a desired length,particularly its minimal length Hmin in instances where thetolerance-elimination element 50 has an uneven length, as is explainedherein.

Depending on the process, materials, and design of the housing beingconstructed, the minimal length Hmin of the tolerance-eliminationelement 50 can generally range from 1 mm to about 20 mm, morespecifically from about 2 mm to about 15 mm, and even more specificallyfrom about 3 mm to about 10 mm. The maximal length Hmax can range fromabout 10 mm to about 30 mm and more specifically from about 15 mm toabout 25 mm. An average length H of the tolerance-elimination element 50can range from about 3 mm to about 20 mm and more specifically fromabout 5 to about 10 mm.

In the exemplary embodiment of FIG. 9A, the solidifiedtolerance-elimination element 50 has a constant length H, FIGS. 9C and9D. Thus, a resulting length LS2 of the intermediate part 45 will becomposed by the length LS1 of the solidified first component 41 and thelength H of the solidified tolerance-elimination element 50 attached tothe end of the first component 41. It should be noted that the lengthH/Hmax/Hmin of the tolerance-elimination element 50 is measured parallelto the longitudinal axis and from the first component's end that isadjacent to the tolerance-elimination element 50, even though in someembodiments the second material 42 a, which forms thetolerance-elimination element 50, can overmold at least a portion of thelongitudinally extending surface of the first component 41 adjacent toits end, as is shown in the exemplary embodiment of FIG. 7A.

Therefore, when the intermediate component 45 is being overmolded by athird plastic material 43 a in a third mold 30 (FIG. 9A), a manufacturercan rely on a very small lengthwise tolerance for the purposes of thisstep. This very small lengthwise tolerance is a result of the very smalllengthwise shrinkage of the tolerance-elimination element 50—andconsequently a very small lengthwise shrinkage of the intermediateportion 45 being overmolded by the third plastic material 43 a. Thelength of the finished multi-component housing is at least three timesgreater than its maximal orthogonal dimension Hmax.

A third component 43, formed by the solidified third plastic material 43a, may have any suitable wall thickness, which may be constant oralternatively may vary throughout the third component 43. In oneexemplary embodiment, particularly suitable for a multi-componenthousing designed for a toothbrush handle, the third component 43comprising a TPE material may have a thickness of from about 0.4 mm toabout 2.5 mm, and more specifically from about 0.7 mm to about 1.4 mm.The intermediate part 45, likewise, may have any suitable, constant orvarying, wall thickness.

In one exemplary embodiment, particularly suitable for a multi-componenthousing designed for a toothbrush handle, the intermediate component 45may have a thickness of from about 1.6 mm to about 5.0 mm. The finishedhousing, comprising at least the first, second, and third plasticmaterials, may have any suitable wall thickness, which may be eitherconstant or vary. In one exemplary embodiment, particularly suitable fora multi-component housing designed for a toothbrush handle, themulti-component housing may have a combined thickness of from about 2.4mm to about 7.5 mm, and more specifically from about 2.0 mm to about 3.5mm, particularly in those parts of the housing that comprise two, three,or more layers of plastic materials.

An enlarged fragmental view of FIG. 9B illustrates an embodiment inwhich the third plastic material 43 a completely overmolds the outersurface of the tolerance-elimination element 50 and extends beyond adistal end 52 of the tolerance-elimination element 50 to at leastpartially cover the surface of the distal end 52 of thetolerance-elimination element 50. As is pointed out in the context ofthe embodiment of FIG. 8B, in such instances the third plastic material43 a can form a touch-up distance from about 0.5 mm to about 3 mm beyondthe end of the intermediate part 45, thereby beneficially forming atouch-up portion or portions. In the embodiments of FIGS. 7-9A interiorwalls of the intermediate part 45 are formed mainly by the material ofthe first component 41, which contacts a portion of the core 15 that islonger than a portion contacted by the second component 42 and/or thethird component 43.

FIGS. 14-17 show several exemplary embodiments of thetolerance-elimination element 50 to illustrate that any conceivableshape thereof can be had as long as it is suitable for the design of themulti-component housing 100 being constructed. In the embodiment of FIG.14, both the proximal end 51 and the distal end 52 of thetolerance-elimination element 50 are straight and inclined relative tothe longitudinal axis of the multi-component housing (the latter notshown for convenience). In the embodiment of FIG. 15, the proximal end51 comprises a concave portion and a straight portion, while the distalend 52 is shaped convexly. In the embodiment of FIG. 16, the proximalend 51 comprises a straight portion disposed between two opposite curvedportions, while the distal end 52 is substantially perpendicular to thelongitudinal axis. In the embodiment of FIG. 17, the proximal endcomprises two straight portions, one of which is perpendicular to thelongitudinal axis of the housing and the other is inclined relativethereto, while the distal end 52 is concave. In the embodiment of FIG.18, each of the proximal end 51 and the distal end 52 comprises aconcave shape, wherein portions having maximal length Hmax are disposedopposite to one another, and portions having minimal length Hmin arelocated on the circumference at about 90 degrees relative to theportions having the maximal length Hmax.

The disclosed process can be successfully utilized for themass-production of small electronic appliances, such as, e.g., variouselectric tools and personal-care implements, including toothbrushes,particularly power toothbrushes. In one aspect, a process of thedisclosure is directed to making a multi-component housing for a handleof a toothbrush 300, such as, e.g., an exemplary power toothbrush shownin FIG. 22. As is known in the art, a handle of a power tool, such as apower toothbrush, typically serves as a housing for an electric motor,battery, wiring, various electronics, and other driving elements used insuch devices. The exemplary power toothbrush 300, shown in FIG. 22,includes a handle 310, comprising a multi-component housing 100 of thedisclosure, and a replaceable refill element 320 that includes a movablehead 330 having cleaning elements.

FIGS. 19-21 show, in perspective or axonometric views, several stages ofconstruction of one specific embodiment of a multi-component housing 100being made for a handle of a power toothbrush, an exemplary embodimentof which is schematically shown in FIG. 22. FIG. 19 shows a partiallymade housing comprising a first component 141 made of a first plasticmaterial. FIG. 20 shows an intermediate part 145 comprising the firstcomponent 141 attached to a second component 142 made of a secondplastic material, wherein the second component 142 includes atolerance-elimination element 150. FIG. 21 shows a finished housing 100comprising the intermediate part 145 partially covered with a thirdcomponent 143 made of a third plastic material, wherein the thirdplastic material completely overmolds an outside surface of thetolerance-elimination element 150.

The first hard-plastic material 141 and the second hard-plastic material142 may differ from one another in at least one characteristic selectedfrom the group consisting of color, opacity, porosity, and hardness. Insome embodiments, at least one of the first hard-plastic material 141and the second hard-plastic material 142 can be transparent ortranslucent, while the soft material can be opaque. In one specificembodiment, the first component 141 can comprise a first hard-plasticmaterial, such as, e.g., a first polypropylene material, the secondcomponent 142 can comprise a second hard-plastic material, such as,e.g., a second polypropylene material, and the third component 143 cancomprise a soft material, such as, e.g., thermoplastic elastomer. Thefirst component 141 can be transparent or translucent; the secondcomponent 142 can be translucent or opaque; and the third component 143can be opaque.

It should be understood that other plastic materials/components can beutilized in the construction of the multi-component housing, if suchmaterials are required. For example, a fourth and/or fifth and/or sixthplastic material or materials can be used in some embodiments to formadditional elements of the housing being made. In the context of a powertoothbrush, e.g., a fourth plastic material can be used for sealingcontrol buttons disposed on the toothbrush's handle. The fourth (fifth,sixth, et cetera) plastic material or materials can be identical to atleast one of the first, second, and third plastic materials—oralternatively can be different from either one of those.

In the context of mass production, the process of the disclosure, whichutilizes the formation of a tolerance-elimination element in amulti-component housing being manufactured, allows manufacturers to relyon very small lengthwise dimension variations of the multi-componenthousing, and therefore very small lengthwise tolerances, among theindividual multi-component housings being produced.

For a great majority of multi-component housings having a nominaloverall length of from about 120 mm to about 200 mm and constructed toform, e.g., handles of power toothbrushes or other power tools, themulti-component housings are expected to have a lengthwise tolerance offrom 0.01 mm to 0.05 mm in absolute numbers. Assuming that in someinstances lengthwise dimension variations among the individual housingsmay constitute opposite deviations, e.g., +0.05 mm in one housing and−0.05 mm in another, lengthwise maximal dimension variations of theoverall lengths among the individual multi-component housings areexpected to be not greater than 0.1 mm. In relative terms, themulti-component housings are expected to have a lengthwise tolerance offrom about 0.006% to about 0.03% relative to the nominal overall lengthof the multi-component housing, and lengthwise maximal variations inlength of from about 0.012% to about 0.06% among the individualhousings.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,each such dimension is intended to mean both the recited value and afunctionally equivalent range surrounding that value, unless otherwisespecified. For example, a dimension disclosed as “10 mm” is intended tomean “about 10 mm.”

The disclosure of every document cited herein, including that of anycross-referenced or related patent or application, is herebyincorporated herein by reference in its entirety unless expresslyexcluded or otherwise limited. The citation of any document is not anadmission that it is prior art with respect to any invention disclosedor claimed herein or that it alone, or in any combination with any otherreference or references, teaches, suggests or discloses any suchinvention. Further, to the extent that any meaning or definition of aterm in this document conflicts with any meaning or definition of thesame term in a document incorporated by reference, the meaning ordefinition assigned to that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A multi-component housing for a toothbrushhandle, the housing having a top end, a bottom end opposite to the topend, and a longitudinal axis therebetween, the housing having a length Lof from about 120 mm to about 200 mm extending between the top andbottom ends and a maximal orthogonal dimension Dmax extendingperpendicular to the longitudinal axis, wherein the length L of thehousing is at least three times greater than the maximal orthogonaldimension Dmax extending perpendicular to the longitudinal axis, thehousing comprising: at least a first component made of a firsthard-plastic material and having a first end and a second end oppositethereto, a second component made of a second hard-plastic material, anda third component made of a soft-plastic material, the first component,the second component, and the third component being integrally joinedtogether to form a generally tubular structure; wherein the housingincludes at least one tolerance-elimination element made of the secondhard-plastic material and attached to one of the first and second endsof the first component along the longitudinal axis, wherein thetolerance-elimination element has a proximal end adjacent to the firstcomponent and a distal end opposite to the proximal end, wherein thetolerance-elimination element has an average length H of from about 3 mmto about 20 mm extending parallel to the longitudinal axis between theproximal end and the distal end of the tolerance-elimination element,wherein an interface between the tolerance-elimination element and theone of the first and second ends of the first component to which end thetolerance-elimination element is attached is oblique relative to thelongitudinal axis, wherein the tolerance-elimination element and thefirst component are at least partially overmolded by the soft-plasticmaterial.
 2. The housing of claim 1, wherein the first hard-plasticmaterial differs from the second hard-plastic material in at least onecharacteristic selected from the group consisting of color, opacity,porosity, and hardness.
 3. The housing of claim 1, wherein the firsthard-plastic material is substantially identical to the secondhard-plastic material.
 4. The housing of claim 1, wherein at least oneof the first hard-plastic material and the second hard-plastic materialis at least partially transparent or translucent and the other one isopaque.
 5. The housing of claim 4, wherein the soft-plastic material isopaque.
 6. The housing of claim 5, wherein the tolerance-eliminationelement is completely overmolded by the soft-plastic material.
 7. Thehousing of claim 6, wherein the soft-plastic material extends beyond thedistal end of the tolerance-elimination element to a distance of fromabout 0.5 mm to about 3 mm therefrom.
 8. The housing of claim 1, whereinthe second hard-plastic material at least partially overmolds the firsthard-plastic material.